Prior art active detection of targets with echo ranging sonar is effective for locating and tracking targets but the target being hunted can detect the signals transmitted by the sonar transducer of the hunting vessel. Accordingly, the personnel on the hunted ship will be aware that they are being tracked.
Heretofore, passive methods of determining a target position or the location of a noise source required the use of expensive and bulky directional hydrophones located at widely separated positions. If it was possible to determine that each hydrophone was receiving noise from the same source, bearing lines were plotted from each hydrophone position to obtain a fix. Since the bearing resolution of directional hydrophones is poor, the fixes obtained involved substantial errors. Furthermore, the target had to provide noise of high intensity to provide an identifiable and usable signal.